Accounting for unintended moisture sources in hygrothermal building analysis

Moisture control analysis of building envelope components by hygrothermal simulation is state-of-theart today and widely applied by architects and engineers. Compared to simple dew-point calculations, transient simulations according to existing standards (e.g. EN 15026-2009) have greatly improved the possibilities of moisture control analysis. However, the underlying assumption of building components without imperfections have remained a weak point, because unintended moisture sources due to e.g. rain-water penetration or air convection may have significant effects in real life. The new draft of the WTA guideline 6-2, whose original version served as blue-print for EN 15026, takes hygrothermal simulations a step further by introducing auxiliary models that account for unintended moisture sources likely to occur in building components, assembled and installed in best practice manner. Because bad workmanship is ruled out, applying these models offers the opportunity to differentiate between design errors and installation failures. Other guideline improvements include new boundary condition aspects such as safety margins for indoor climate conditions and consideration of envelope shading. Since capillary active insulation materials have become more popular in recent years a more accurate determination of liquid transport characteristics is also proposed. The new items in WTA 6-2 are summarized and their impacts on hygrothermal simulation results are discussed.